1. Field of the Invention
This invention relates to a multi-layered printed wiring board having a plurality of wiring layers, and more particularly to a multi-layered printed wiring board that is suitably applied to achieve high-density wiring.
2. Description of the Related Art
In recent years, with the advancement of functions of digital equipment, an increasing number of printed wiring boards installed on digital equipment have been equipped with a great number of multi-pin packaged semiconductor devices such as the BGA (Ball Grid Array). Such multi-pin packaged semiconductor devices include integrated circuits having 500 pins or more. The wiring density of such printed wiring boards has been raised with the increase in the number of pins. This necessitates increasing the number of wiring layers of printed wiring boards, and if a multi-layered printed wiring board having four layers cannot house all required lines, a multi-layered printed wiring board having six layers or a multi-layered printed wiring board having eight layers is used.
Japanese Laid-open Patent Publication (Kokai) No. 10-270862 discloses an example of conventional multi-layered printed wiring boards (first prior art). According to this prior art, a plurality of circuit elements are mounted on the multi-layered printed wiring board, and a ground layer, a signal layer, and a power supply layer providing the circuit elements with power supply voltages are laminated one upon another via respective insulating materials. The respective circuit elements are classified into a plurality of groups according to the operating speed, and regions for mounting the circuit elements on the multi-layered printed wiring board are determined according to the groups. In the power supply layer, power supply lines are formed according to the groups, and a power line, which separates the power supply lines from one another against high frequencies, connects between the power supply lines belonging to different groups. In this connection, the multi-layered printed wiring board must be provided with a ground-only layer comprised only of ground lines and a power supply-only layer comprised only of power supply lines in order to reduce radiation noises.
Further, Japanese Laid-open Patent Publication (Kokai) No. 7-321429 discloses an example of conventional double-layered printed wiring boards (second prior art). In the printed wiring board according to this prior art, ground lines and power supply lines are provided in the form of a grid in each of the wiring layers such that they extend in parallel and are alternately arranged, and the wiring layers are arranged such that the lines of a first wiring layer and those of a second layer vertically intersect each other, and the ground lines and the power supply lines in the respective wiring layers are connected together via through holes. This arrangement enables a solid ground and reduces radiation noises.
The above described prior arts, however, have the following problems:
The increase in the number of layers as in the first prior art to accommodate all required lines easily realizes high-density wiring, but increases the time and cost required for manufacturing the printed wiring board.
Providing ground lines and power supply lines in the form of a grid on each of the wiring layers as in the second prior art reduces radiation noises, but imposes a lot of restrictions on a space for wiring signal lines and makes it difficult to achieve high-density wiring.
It is therefore an object of the present invention to provide a multi-layered printed wiring board that is capable of securing required wiring density even with a decreased number of wiring layers and reducing radiation noises.
To attain the above object, a first aspect of the present invention provides a multi-layered printed wiring board having at least three wiring layers each at least having at least one power supply line or a ground line, and another kind of line, said wiring layers each having an outer edge, comprising the ground line formed at the outer edge of at least one of the wiring layers, a basic power supply line formed inside the ground line, the at least one power supply line extending from the basic power supply line, a plurality of electronic parts mounted on at least one of the wiring layers, and wherein the at least one power supply line is wired to mounting positions of the electronic parts via at least one of the wiring layers.
Preferably, the ground line and the basic power supply line are each shaped substantially in a form of annulus and arranged adjacent to each other.
Preferably, the multi-layered printed wiring board according to the first aspect comprises a signal line provided in each of the wiring layers, the signal line connecting between ones of the electrical parts mounted on one of the wiring layers or connecting between ones of the electrical parts mounted on respective different ones of the wiring layers via at least one of the wiring layers, and wherein the power supply line and the signal line are formed inside the basic power supply line.
To attain the above object, a second aspect of the present invention provides a multi-layered printed wiring board having at least three wiring layers each at least having at least one power supply line or a ground line, and another kind of line, said wiring layers each having an outer edge, comprising the ground line formed at the outer edge of at least one of the wiring layers, a plurality of electronic parts mounted on at least one of the wiring layers, the at least one power supply line provided in a predetermined one of the wiring layers at a location inside the ground line, the at least one power supply line being wired to mounting positions of the electronic parts via at least one other one of the wiring layers, a signal line provided in each of the wiring layers, the signal line connecting between ones of the electrical parts mounted on one of the wiring layers or connecting between ones of the electrical parts mounted on respective different ones of the wiring layers via at least one of the wiring layers, and a ground pattern formed over a region other than the power supply line and the signal line and connected to the ground line.
Preferably, in the multi-layered printed wiring board according to the second aspect, the ground line and ground pattern are formed such that the ground line and ground pattern substantially entirely cover the multi-layered printed wiring board when the ground line and ground pattern are projected on one projection plane.
Also preferably, the multi-layered printed wiring board according to the second aspect comprises a basic power supply line formed at the outer edge of at least one of the wiring layers at a location adjacent to and inside the ground line, wherein the power supply line is formed inside the basic power supply line and extends from the basic power supply line via at least one of the wiring layers such that the power supply line is wired to mounting positions of the electrical parts, and the signal line is formed inside the basic power supply line, the signal line connecting between ones of the electrical parts mounted on one of the wiring layers or connecting between ones of the electrical parts mounted on respective different ones of the wiring layers via at least one of the wiring layers.
Preferably, in the multi-layered printed wiring board according to the second aspect, the ground line and the basic power supply line are each shaped substantially in a form of annulus and arranged adjacent to each other.
Preferably, in the multi-layered printed wiring board according to the second aspect, the power supply line and the power supply line are arranged so as not to overlap the power supply line and the signal line in at least one other one of the wiring layers which is adjacent to the at least one of the wiring layers in which the power supply line is formed, when the power supply lines and the signal lines are projected on one projection plane.
To attain the above object, a third aspect of the present invention provides a multi-layered printed wiring board having at least three wiring layers each at least having at least one power supply line or a ground line, and another kind of line, said wiring layers each having an outer edge, the multi-layered printed wiring board comprising a first wiring layer constituting one of the wiring layers, and having ground line formed at the outer edge of the first wiring layer, a first basic power supply line formed adjacent to and inside the ground line, and a first power supply line extending from the first basic power supply line, a second wiring layer constituting one of the wiring layers, and having a ground pattern formed at the outer edge of the second wiring layer, a second basic power supply line for supplying a different voltage from a voltage supplied by the first basic power supply line, the second basic power supply line being formed at a position where the first basic power supply line is projected when the second basic power supply line and the first basic power supply line are projected on one projection plane, and a second power supply line extending from the second basic power supply line, and a plurality of electronic parts mounted on at least one of the wiring layers, wherein the first and second power supply lines extending from the first and second basic power supply lines, respectively are wired to mounting positions of the electronic parts via at least one of the wiring layers.
Preferably, in the multi-layered printed wiring board according to the third aspect, the ground line and ground pattern and the first and second basic power supply lines are each shaped substantially in a form of annulus.
Also preferably, the multi-layered printed wiring board according to the third aspect comprises a signal line provided in each of the wiring layers, the signal line connecting between ones of the electrical parts mounted on one of the wiring layers or connecting between ones of the electrical parts mounted on respective different ones of the wiring layers via at least one of the wiring layers, and a ground pattern formed over a region other than the first and second power supply lines and the signal line and connected to the ground line and ground pattern, and wherein the first and second power supply lines and the signal line are formed inside the first and second basic power supply lines.
To attain the above object, a fourth aspect of the present invention provides a multi-layered printed wiring board having at least three wiring layers each at least having at least one power supply line or a ground line, and another kind of line, said wiring layers each having an outer edge, comprising the ground line formed at the outer edge of at least one of the wiring layers, a first basic power supply line formed adjacent to and inside the ground line, a second basic power supply line formed adjacent to and inside the ground line to supply a different voltage from a voltage supplied by the first basic power supply line, at least two power supply lines extending from respective ones of the first and second basic power supply lines, a plurality of electronic parts mounted on at least one of the wiring layers, and wherein the power supply lines are wired to mounting positions of the electronic parts via at least one of the wiring layers.
Preferably, in the multi-layered printed wiring board according to the fourth aspect, the ground line and the first and second basic power supply lines are shaped substantially in a form of annulus.
Also preferably, the multi-layered printed wiring board according to the fourth aspect comprises a signal line provided in each of the wiring layers, the signal line connecting between ones of the electrical parts mounted on one of the wiring layers or connecting between ones of the electrical parts mounted on respective different ones of the wiring layers via at least one of the wiring layers, and a ground pattern formed over a region other than the power supply lines and the signal line and connected to the ground line, and wherein the power supply lines and the signal line are formed inside the second basic power supply line.
To attain the above object, a fifth aspect of the present invention provides a multi-layered printed wiring board having at least three wiring layers each at least having at least one power supply line or a ground line, and another kind of line, said wiring layers each having an outer edge, comprising the ground line formed at the outer edge of each of the wiring layers, a basic power supply line formed adjacent to and inside the ground line in each of the wiring layers, a plurality of electronic parts mounted on at least one of the wiring layers, the at least one power supply line provided in at least one of the wiring layers at a location inside the basic power supply line, the at least one power supply line extending from the basic power supply line via at least one other one of the wiring layers and wired to mounting positions of the electronic parts, a signal line provided in each of the wiring layers, the signal line connecting between ones of the electrical parts mounted on one of the wiring layers or connecting between ones of the electrical parts mounted on respective different ones of the wiring layers via at least one of the wiring layers, and a ground pattern formed over a region other than the power supply line and the signal line at a location inside the basic power supply line in at least one of the wiring layers, and wherein the ground line in at least one of the wiring layers has a width greater than the ground line in the other wiring layers and connected to the ground pattern via at least one through hole.
In the multi-layered printed wiring board according to the present invention, the ground line is formed at the outer edge of at least one of the wiring layers and the basic power supply line is formed inside the ground line, and the power supply line and the signal line extend from the basic power supply line to mounting positions of the electronic parts via at least one of the wiring layers. This enables higher-density wiring without lowering the wiring density compared with a multi-layered printed wiring board having a ground-only layer and a power supply-only layer.
Further, since the power supply line and the signal line are wired inside the annular basic power supply line in the wiring layer or layers in which they are provided, the degree of freedom in wiring signal lines can be increased.
Further, since the basic power supply line and the ground line are annular in shape and wired adjacent to each other, the capacitive connection between the basic power supply line and the ground line is improved to reduce radiation noises.
Further, in the wiring layer or layers in which the power supply line and the signal line are provided, the ground patterns are formed over a region other than the signal line and the power supply line, and are connected together via through holes. This forms stable grounding and reduces radiation noises.
Further, the ground lines and ground patterns in the respective different wiring layers cover the entire surface of the multi-layered printed wiring board when they are projected on the same projection plane. This forms more stable grounding and reduces radiation noises.
Further, since the signal line and the power supply line are wired at such positions that they do not overlap the signal lines and the power supply lines in adjacent wiring layers when they are projected on the same projection plane. This reduces the effect of cross talk.
Further, since the ground lines in the respective different wiring layers are connected together via through holes, radiation noises can be satisfactorily reduced without providing a ground-only layer.
Therefore, the multi-layered printed wiring board according to the present invention is capable of reducing radiation noises without lowering the wiring density even if the number of wiring layers is decreased.
The above and other objects of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.